Food referred to as so-called health foods is in many cases prepared as small-size solid materials in the form of pellets, granules, tablets or the like, for example, from the point of view of easiness for management of amounts of food to be eaten and for the filling in containers or the like, unlike usual food people eats daily. These small-size foods are currently on the market in such a state that they are processed into products without coating their surfaces.
Some of these small-size foods are likely to become powder upon being subjected to an impact, when they have low surface strengths. Some small-size foods are prone for their active ingredients to deteriorate due to oxidation. Further, it sometimes causes to happen that foods smell undesirable or unpleasant.
It is desired, accordingly, that these small-size foods be coated at their surfaces with a coating layer of a polymer substance.
At the present time, however, no method of coating has been yet developed that can form a highly safe coating of a polymer substance on these small-size foods with high efficiency and at low costs.
On the other hand, a spray coating is known to the art that can form a coating of a polymer substance on the surfaces of small-size solid materials with high efficiency. The spray coating involves spraying small-size solid materials in a movable state with a solution of a polymer substance. It can be noted herein that the factor exerting the biggest influences on efficiency in preparation of products and costs of production thereof is a selection of a polymer substance to be sprayed in the form of a solution. Therefore, the selection of the polymer substance is the greatest problem to be solved.
As a result of extensive research and review, it has been found by the present inventors that polymeric substances, such as guar gum, gum traganth, xanthane gum, carrageenan, tamarind gum, locust bean gum, sodium carboxymethyl cellulose, sodium carboxymethyl starch and sodium alginate, are too high in viscosity in the form of an aqueous solution so that their spray coating characteristics are too poor to be practically applied. In order to make these natural polymer substances in the form of a solution having a relatively low viscosity appropriate for spray coating, it is necessary to make the polymer substance in the concentration as extremely low as 2% or lower. The solution having the polymer substance in such a low concentration suffers from the extremely great difficulty in the formation of a continuous coating layer having high durability. Further, the such solution requires a long period of time for drying a coating and it remarkably reduces efficiency in the preparation of products.
Further, natural polymer substances such as gum arabic, pullulan, gelatin and so on, are so high in viscosity that the products coated with such a natural polymer substance are prone to attach to each other, resulting in the formation of an aggregate with no commercial value.
On the other hand, for a pharmaceutical preparation, it is desired to develop a method of spray coating using an aqueous solution of a highly safe natural polymer substance. At the present time, however, no such a spray coating method has been developed yet.
The major object of the present invention is to provide a method for forming a highly safe coating of a natural polymer substance on surfaces of small-size foods or pharmaceutical preparations by spray coating with high production efficiency and at low production costs.
Another object of the present invention is to provide small-size foods and pharmaceutical preparations with a highly safe coating of a natural polymer substance coated on their surfaces.
Other objects, features and advantages will become apparent in the course of the description of the specification that follows.